Layered products in which a gas barrier layer containing aluminum or aluminum oxide as a component is formed on a plastic film have been conventionally well-known. Such layered products are used as packaging materials for protecting articles (such as foods) which are susceptible to quality change induced by oxygen. In many cases, such a gas barrier layer is formed on a plastic film by a dry process such as physical or chemical vapor deposition. Aluminum-deposited films have light shielding properties as well as gas barrier properties and are typically used as packaging materials for dry foods. Aluminum oxide-deposited films, which have transparency, are characterized by allowing visual recognition of contained substances and by enabling check for foreign matters with a metal detector and heating with a microwave oven. These films are thus used as packaging materials in a wide variety of applications such as retort food packaging.
For example, Patent Literature 1 discloses a gas barrier layer containing aluminum, the gas barrier layer being a transparent gas barrier layer composed of aluminum atoms, oxygen atoms, and sulfur atoms. Patent Literature 1 discloses a method for forming the transparent gas barrier layer by reactive sputtering.
Patent Literature 2 discloses a transparent gas barrier layer composed of a reaction product of aluminum oxide particles and a phosphorus compound. Patent Literature 2 discloses a method for forming the gas barrier layer, in which a coating liquid containing aluminum oxide particles and a phosphorus compound is applied onto a plastic film, then dried and heat-treated.
The conventional gas barrier layers have good gas barrier properties; however, many of these gas barrier layers have high surface electrical resistivities. It is difficult to use such a gas barrier layer having a high surface electrical resistivity in applications that require antistatic performance as well as gas barrier properties. When dried bonito shavings are put into a conventional vertical form-fill-seal bag, the powdery shavings contained in the bag adhere to the inner and outer surfaces of the bag due to static electricity, which may cause the shavings to be caught in a sealed portion or a sealer to be contaminated by the shavings during heat sealing. In addition, when the sealed bag is opened to remove the shavings, they cannot be removed smoothly from the bag, which causes the shavings to adhere to the periphery of the opening of the bag.
Patent Literature 3 discloses a gas-barrier in-mold label having an antistatic layer. Patent Literature 3 describes that the in-mold label has water vapor barrier properties. However, Patent Literature 3 fails to indicate whether or not the in-mold label has oxygen barrier properties.